And of course, some of her support among conservatives might be because they think she'll do poorly in a general election, increasing the chances that the Republicans take back control of the White House.

While Clinton has continued to insist that she is done with public service once she retire from the State Department next year, those kinds of denials are pro forma for future candidates. There's really no way she'll be able to convince anyone she's actually out of the race until someone else gets nominated.

She's the most popular choice for the Democrats in 2016, so the pressure will only get more intense from here.

Clinton is a former senator and first lady, who came a narrow second to Obama in a bid for the Democratic nomination. She has very heavy support on both sides of the aisle, and she has been acclaimed by both Democrats and Republicans in her role as America's foremost ambassador.

She also has the support of her husband, former President Bill Clinton, who has become a celebrity among Democrats.

Clinton would also continue the streak of historic firsts for the Democrats, following the first African-American president with the first female president.

That will provide ammunition against anyone the Republicans front in 2016, which could include Marco Rubio, who would be the first Hispanic presidential candidate, or perhaps even a woman of their own.